Download 03 Absorption in gastrointestinal tract and motility of gastrointestinal

Absorption in
gastrointestinal tract and
motility of
gastrointestinal tract
Determine of notion “absorption”
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Absorption is a complex of processes, which
are provide transport of substances from
digestive tract into internal surroundings of
organism (blood, lymph, intercellular
substances)
Main types of transport of nutritive substances in
internal surroundings of organism
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1. Passive: diffusion and osmosis. This transport do
not need presents of energy. In this case substances
transport through the mucus shell by help of
concentrative gradient. This way of transport have
water, water dissolved vitamins (C, B6, B2).
2. Active: pinocytosis and active transport by help of
protein and energy. Active transport need energy of
ATP. This way characteristic of amino acids,
monosaccharide, vitamin B12, ions of calcium,
enzymes. Pinocytosis – by help of pinocytic bulb,
where secreted enzymes for proteins hydrolysis.
Products of hydrolysis adsorbed by cell.
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The total quantity of fluid that must be
absorbed each day is equal to the ingested fluid
(about 1,5 liters) plus that secreted in the
various gastrointestinal secretions (about seven
liters). This comes to a total of approximately
8 to 9 liters. All but 1,5 liters of this is
absorbed in the small intestine, leaving only
1,5 liters to pass through the ileocecal valve
into the colon each day.
Absorption in intestines
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Small intestines has a big length – 3-8 meters; large
quantity of substances absorbed in a middle part of
small intestines; common surface of intestines – 200
m2. The structure bases of absorption in small
intestines are villi. In large intestines absorbed water
and completed absorption of a small quantity of
hydrolytic substances of carbohydrates, proteins and
lipids. By help of this way may absorbed components
of nutritive elements (glucose, vitamins, water etc).
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The Absorptive Surface of the Intestinal
Mucosa – The Villi. The absorptive surface of
the intestinal mucosa, showing many folds
called valvulae connivances (or folds of
Kerckring), which increase the surface area of
the absorptive mucosa about threefold. These
folds extend circularly most of the way around
the intestine and are especially well developed
in the duodenum and jejunum, where they
often protrude as much as 8 mm into the
lumen.
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The intestinal epithelial cells are characterized
by a brush border, consisting of about 600
microvilli 1 μm in length and 0,1 μm in
diameter protruding from each cell. This
increases the surface area exposed to the
intestinal materials another 20-fold. Thus, the
combination of the folds of Kerckring, the
villi, and the micro villi increases the
absorptive area of the mucosa about 600-fold,
making a tremendous total area of about 250
square meters for the entire small intestine –
about the surface area of a tennis court.
ABSORPTION IN THE SMALL
INTESTINE

Normally, absorption from the small intestine each
day consists of several hundred grams of
carbohydrates, 100 or more grams of fat, 50 to 100
grams of amino acids, 50 to 100 grams of ions, and 7
to 8 liters of water. However, the absorptive capacity
of the small intestine is far greater than this as much
as several kilograms of carbohydrates per day, 500 to
1000 grams of fat per day, 500 to 700 grams of amino
acids per day, and 20 or more liters of water per day.
In addition, the large intestine can absorb still more
water and ions, though almost no nutrients.
ABSORPTION IN THE LARGE
INTESTINE
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Approximately 1500 ml of chyme pass through the
ileocecal valve into the large intestine each day. Most
of the water and electrolytes in this are absorbed in
the colon, usually leaving less than 100 ml of fluid to
be excreted in the feces. Also, essentially all the ions
are also absorbed, leaving only about 1 mEq each of
sodium and chloride ions to be lost in the feces.
Most of the absorption in the large intestine occurs in
the proximal half of the colon, giving this portion the
name absorbing colon, whereas the distal colon
functions principally for storage and is therefore
called the storage colon.
Regulation of absorption

Absorption regulated by nervous system, for
example by cortex; by vegetative nervous
system; endocrine glands, for example
adrenocorticotropin, aldosteron,
glucocorticoids, insulin, thyroxin, local factors
of food, for example pepper, mustard.
Peculiarities of absorption of organic
and inorganic substances
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Water and mineral salts
Products of proteins hydrolysis
Products of carbohydrates hydrolysis
Products of fats hydrolysis
Mineral salts
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Sodium transport in two stages: passive
(sodium go through the apical part of
enterocytes membrane from chyme) and active
(sodium go by help of Na+,K+-ATPase on
base-lateral part of enterocytes membrane in
blood). Chloride and HCO3- go together with
sodium. Ca2+, Mg2+ absorbed actively.
That the transport of most monosaccharide through
the intestinal membrane is an active process is
demonstrated by several important experimental
observations:
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1. Transport of most of them, especially glucose and
galactose, can be blocked by metabolic inhibitors,
such as iodoacetic acid, cyanides, and phlorhizin.
2. The transport is selective, specifically transporting
certain monosaccharide without transporting others.
The order of preference for transporting different
monosaccharide and their relative rates of transport in
comparison with glucose are:
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3. There is a maximum rate of transport for each type
of monosaccharide. The most rapidly transported
monosaccharide is galactose, with glucose running a
close second. Fructose, which is also one of the three
important monosaccharide's for nutrition, is absorbed
less than half as rapidly as either galactose or glucose;
also, its mechanism of absorption is different, as will
be explained below.
4. There is competition between certain sugars for the
respective carrier system. For instance, if large
amounts of galactose are being transported, the
amount of glucose that can be transported
simultaneously is considerably reduced.